Technically, in order to reuse rod bolts you need to have the measurements from before they were torqued, so that you can re-measure them and determine if they've stretched beyond their elastic limit. I think machine shops will usually give you the measurements when they assemble a motor for you (dunno, I've done it myself the two times I've built bottom ends), so you might ask the PO if he's got a set of measurements. Hopefully you've got it marked as to which bolt came out of which hole in the motor?

If not, then you're taking a risk by reusing them. I think rod bolt failures are usually due to tensile loading rather than compressive loading, and detonation is more about compression, so that would argue that as long as they were torqued properly (ideally with a rod bolt stretch gauge, not a torque wrench) they should be fine.

I tried to reuse rod bolts once. I pulled the recorded stretch specs from my assembly notes, measured each one again to verify, and then started disassembly. The fourth rod bolt came out 0.0005" stretched. Had to throw the whole set away anyway.

I tried to reuse rod bolts once. I pulled the recorded stretch specs from my assembly notes, measured each one again to verify, and then started disassembly. The fourth rod bolt came out 0.0005" stretched. Had to throw the whole set away anyway.

Fresh ARP2000 bolts are $75

I know they aren't expensive, but its still money I could have saved. Is 0.0005" really going to effect anything? That seems negligible?

I'll preface this by saying that I'm a software guy, not a mechanical engineer, but here's my understanding:

Metals stretch in two ways -- elastic and plastic. Elastic deformation is like a spring, it deforms in a particular direction under a load and when the load it released it goes back to its original shape. Plastic deformation is a permanent change, when you remove the load it does not return to the original shape. Steel will stretch a small amount in an elastic fashion, and beyond that limit it becomes plastic.

When you torque a bolt, what you are actually doing is stretching it within the elastic range. That's what produces the clamping force, the "spring" of the steel trying to pull the bolt back into its original shape. A torque wrench is only a somewhat accurate way of measuring this because much of the torque goes into overcoming friction. Variances in the cleanliness of the threads, lubrication of the surfaces, etc can change the amount of torque required to get a particular amount of stretch by a fairly large amount.

So when you attach critical fasteners, the best way to do it is to directly measure the stretch of the bolt using a stretch gauge, like this:

The two points go into the dimples on the two ends of the rod bolt and the dial indicator tells you how long it is. For the final tightening you turn the bolt until the length is the specified amount longer than it was at the beginning, typically something like .005-.006 inches. This puts the clamping load into the desired range, but not so high that it plastically deforms the bolt. The rods come with an installation procedure that gives the exact steps for doing this.

Rod bolts need to deal with both static and dynamic loads, though. As the piston moves past the halfway point in the upwards direction it is moving upwards faster than the crank throw. This means that the rod is being stretched by the crank on one end and the piston on the other, and since the rod is in two pieces, all of that stretch is being taken by the rod bolts. This dynamic load is added to the static tensile load that you put on the rod bolts by torquing them, and if that load goes above the elastic limit and into the plastic zone the bolt is permanently stretched and will never be as strong as it was before. When you stretch metal it necks down, becoming thinner and losing some of the strength it needs to resist further deformation. Do that enough times and the rod bolt breaks and boom. If one of the bolts was overtorqued a little bit putting it in (perhaps because the installer used a torque wrench instead of a stretch gauge) then an overrev on the motor may have deformed it.

So yeah, if a rod bolt comes out half a thou longer than it went in, it's junk. If you don't know how long they were before they went in, there's no way to check this because they aren't close enough to each other the factory to go from that spec. I measured mine with a micrometer before they went in, and they ranged between 1.82525 and 1.82735 inches.

"Fatigue damage is caused by the simultaneous
action of cyclic stress, tensile stress,
and plastic strain. If any one of these three is
not present, a fatigue crack will not initiate
and propagate. The plastic strain resulting
from cyclic stress initiates the crack; the
tensile stress promotes crack growth (propagation).
Careful measurement of strain shows
that microscopic plastic strains can be present
at low levels of stress where the strain might
otherwise appear to be totally elastic. Although
compressive stresses will not cause
fatigue, compressive loads may result in local
tensile stresses." ASM article

Last edited by DNMakinson; 11-02-2016 at 08:43 AM.
Reason: Quoted from the long article

Lots of good info here. Thanks guys. I am just going to get new ones because I don't want to risk it. I don't know what the specs were when the rods were new so I can't use them. Oh well.

I got new "premium" front rotors because the stock ones were grooved and just worn out. I didn't get any pics of them due to time (I was in a rush to install everything to to daylight running out, I don't like working in the dark)

I have to say, I am beyond happy with these pads for the street. They dust like stock and are silent, yet the initial bite and overall stopping power is greatly improved. I will surely be buying another set of these once they wear out.

I'm running the 1x579 and its the best thing since the EFR. The other two in the above image are a little easier if you are building an exhaust because the last bend going into the muffler is not as tight, but I doubt it matters that much in the end.

The big magnaflow is Great. I ordered mine on Amazon and had a local muffler shop cut the small can off my Enthuza and replace it with this one. The Enthuza exhaust is a great piece, well made, but my car was loud enough that I'd set off alarms while slowly driving through the parking garage at my office. I even added added a resonator and it still wasn't quiet enough. The big manglaflow is amazing, now the car is basically 100% stealth.

The big magnaflow is Great. I ordered mine on Amazon and had a local muffler shop cut the small can off my Enthuza and replace it with this one. The Enthuza exhaust is a great piece, well made, but my car was loud enough that I'd set off alarms while slowly driving through the parking garage at my office. I even added added a resonator and it still wasn't quiet enough. The big manglaflow is amazing, now the car is basically 100% stealth.

You can get the same muffler on Advance Auto's website, use trt41 and get $40 off the order.

Does that work for stuff other than mufflers? Might be time to order a spare O2 sensor.

I love me some quiet exhaust and I should point out I'm running the Magnaflow 1x579 AND a Vibrant 17950 great big sonnovabitch 3" resonator. I posit that I have the quietest, stealthiest, free flowingist exhaust <clarkson> ...in the world.</clarkson> The fact that I'm running that resonator is a testament to gesso's ability as a fabricator.